Position sensing for moveable mechanical systems and associated methods and apparatus

ABSTRACT

Position sensing of movable elements including but not limited to machine components is disclosed. Motion of a movable element can produce motion of a magnetic field, which can be detected by magnetic sensors. The motion and/or variations of a magnetic field and/or a magnetic flux may be produced by any combination of a motion of the sensors, associated magnets, or associated magnetic material. Magnetic sensors maybe capable of measuring either rotary, or linear motion, or both. Such sensors can provide indication of an incremental position change, an absolute position, or both. Absolute position and high-resolution position sensing may be produced for measurement of either linear and/or angular motion. Suitable magnetic sensors include, but are not limited to, Hall effect devices and/or magneto-resistive elements, and may include multi-element magnetic sensors. Suitable signal conditioning and/or control means such as control electronics can be used to receive output signals from the sensors.

BACKGROUND

Position sensors are commonly used to measure the position of variouselements of a movable mechanical system. Such systems often include oneor more actuators, which typically include a motor and output drivetrain, to provide the desired linear or rotary motion. These actuatorsare commonly electromagnetic, piezoelectric, pneumatic, and hydraulicactuators. These systems may also include position feedback sensors andcircuitry as part of the associated actuator system, and may be referredto as servoactuators or servocontrol systems.

Position sensors for mechanical systems typically measure thedisplacement of an element of an actuator or a component moved by suchan element. In some systems, magnetic sensors are used as to sense theposition of the desired components. Two classes of such magnetic sensorsare Hall effect sensors and magneto-resistive sensors. Hall effectsensors measure a voltage that is induced in a semiconductor materialdue to the effect of a magnetic field on an electrical current flowingin the semiconductor material, known as a Hall voltage. Hall effectsensors are sometimes referred to as Hall effect elements or Hall effectdevices (HEDs). Magneto-resistive sensors utilize materials that exhibita change in resistance due to the influence of a magnetic field.

One class of Hall effect sensors include digital Hall effect sensors,which typically provide a binary output that is dependent upon thepresence, absence, and/or orientation of a magnetic field. The binaryoutput, also known as the digital Hall state, can be counted and used toindicate the movement of the component of interest that the one or moremagnets are coupled to. In this way, the movement and position of aservoactuator component of interest may be determined. Digital Halleffect devices typically include signal-conditioning circuitry, e.g., aSchmitt inverter, to condition the output signal of an analog HED.

Limitations exist with current techniques of sensing position withmagnetic sensors. Such limitations may be particularly pronounced inmovable mechanical systems having complex drive trains. Inaccurateposition measurement can occur when individual magnetic sensors aresubject to ambient environmental factors such a temperature variations,local magnetic field variations, and electromagnetic interference ornoise. Calibration errors in the sensors may also produce or contributeto errors in position measurement.

Inaccurate position measurement can occur in movable mechanical systems,including those with complex drive trains, when one or more magneticsensors are used to measure a single mechanical element that is subjectto back lash or mechanical compliance. For example, backlash andmechanical compliance are not accommodated in a complex drive train by amagnetic sensor used to measure the rotation of an EMA motor shaft usedas a prime mover for the drive train.

SUMMARY

The present invention addresses the previously described limitations.Aspects of the present invention may be used to detect motion of movableelements including but not limited to machine components of moveablemechanical systems. Motion of a movable element can produce motionand/or variation of a magnetic field of a magnet relative to a magneticsensor. By sensing the motion of two or more moveable elements of amoveable mechanical system the determination of position of associatedmechanical components is improved. The motion and/or variations of amagnetic field and/or a magnetic flux may be produced by any combinationof a motion of the sensors, associated magnets, or associated magneticmaterials interposed between a sensor and an associated magnet. Certainaspects of the present invention are directed to multi-element magneticsensors used for position sensing of movable elements, including but notlimited to machine components. Multi-element sensors according to theinvention may be capable of measuring either rotary or linear motion orboth. The multi-element sensor can provide indication of an incrementalposition change, an absolute position, or both. Certain aspects of thepresent invention provide for a combination of absolute position sensinghigh-resolution position sensing for measurement of either linear and/orangular position. By combining two or more magnetic sensors in amoveable machine assembly, e.g., an actuator, redundant positionmeasurement functionality can be provided or combined at differentlevels of mechanical advantage in the assembly to provide a broaderrange of position measurement, or higher measurement resolution, orboth. Suitable magnetic sensors include; but are not limited to, Halleffect devices and/or magneto-resistive elements. Suitable signalconditioning and/or control means such as control electronics can beused to receive output signals from the sensors. The motion of movableelements, such as mechanical systems including actuators, canaccordingly be measured and controlled. Position signals can be used incertain embodiments for desired control functions. For non-limitingexample, position signals obtained from one or more multi-elementmagnetic sensors can be used to control the commutation of brushless DCmotors, e.g., a motor of an EMA coupled to a drive train.

During position sensing operation, one or more multi-element magneticsensors may provide electric signals to an electronic control unit,which can enable the electronic control unit to control a commutationsequence for a desired brushless DC motor, e.g., an EMA motor. For sucha commutation sequence, the electronic control unit may use one or moreposition signals, each from a different multi-element magnetic sensor,to control output currents to stator coils within the DC motor ofinterest. By switching the currents to the stator coils in a commutationsequence, the currents in the stator coils generate magnetic fields thatproduce torque on a shaft of the rotor associated with the stator,causing the rotor and shaft to rotate to a desired position relative tothe stator.

One embodiment of the present invention includes a position sensingsystem for a drive train having a plurality of moveable drive elements.The system includes a plurality of magnets each of which corresponds oris affixed to one of the plurality of drive elements. The systemincludes a plurality of magnetic sensors each of which are configuredand operable to detect a change in flux density produced by motion of amagnetic field produced by a corresponding one of the plurality ofmagnets. Each magnetic sensor is operable to produce an output signalcorresponding to the motion of the corresponding moveable drive element.Control means are operable to receive the output signals from theplurality of magnetic sensors and combine the output signals. Theplurality of magnets may include multiple-poled magnets, such aseight-poled magnets. The magnetic sensors may include a multi-elementmagnetic sensor. The system electronic control means may be operable toproduce a control signal as an output. The multi-element magnetic sensormay include a plurality of magneto-resistive elements. The plurality ofmagneto-resistive elements may include four magneto-resistive elementsconfigured electrically in a bridge configuration. The bridgeconfiguration may be a Wheatstone bridge. The multi-element magneticsensor may include a plurality of Hall effect elements. The plurality ofHall effect elements may include proportional Hall effect elements. Theplurality of Hall effect elements may include digital Hall effectelements. The plurality of Hall effect elements may include fourproportional Hall effect elements configured and arranged in an IC.

The system may include a high-resolution magnetic sensor and a pluralityof high-resolution magnets having alternating north and south magneticpoles arranged in a desired configuration, and the plurality of magnetsmay be affixed to one of the plurality of movable drive elements. Thehigh-resolution magnetic sensor may be operable to measure magneticfield variations produced by the plurality of high-resolution magnetsduring motion of the movable element. The system may include a toothedmagnetic flux guide adjacent to the high-resolution magnetic sensor andoperable to channel magnetic flux from the plurality of high-resolutionmagnets to the high-resolution magnetic sensor. The high-resolutionmagnetic sensor may include a magneto-resistive element. Thehigh-resolution magnetic sensor may include an analog Hall effectelement. The high-resolution magnetic sensor may include a digital Halleffect element. The desired configuration may be a ring. The desiredconfiguration may be a linear array. The system may include a flux guideaffixed to the moveable element and operable to modulate magnetic fluxat the magnetic sensor. The plurality of drive train elements mayinclude a rotatable shaft, and one or more of the plurality of magneticsensors may include a magnetic quadrature sensor. The magneticquadrature sensor may include two pairs of magnetic yokes adapted to thecircumference of the shaft. The shaft may include a plurality ofmagnets. A respective magnetic sensor may be disposed between ends of arespective pair of the two pairs of magnetic yokes, and the magneticquadrature sensor may be operable to detect motion of the shaft and toproduce as an output a quadrature signal corresponding to the motion.The control means may include an electronic control unit operable toreceive the quadrature signal from the magnetic quadrature sensor and toprovide sine wave quadrature decoding for the quadrature signal todetermine a position of the shaft. The magnetic yokes may include aparamagnetic magnetic material. The magnets may include a magneticmaterial selected from the group consisting of iron, nickel, cobalt,dysprosium and gadolinium.

A further embodiment includes a method of measuring position of amovable element of a drive train having a plurality of movable elements.The method may include producing motion of a movable element of theplurality of movable elements. Motion of a first magnetic field relativeto a first magnetic sensor may be produced by the motion of the moveableelement. Motion of a second magnetic field relative to a second magneticsensor may be produced by the motion of the moveable element. Variationsin the magnetic fields may be detected. An output signal correspondingto the variations in the magnetic fields may be produced, and a positionof the moveable element may be measured. The step of producing motion ofa movable element may include a step of moving an actuator outputelement. The step of producing motion of a magnetic field may include astep of moving a magnet affixed to the movable element. The step ofproducing motion of a magnetic field may include a step of moving thefirst magnetic sensor. The motion of the magnetic field may corresponddirectly to the motion of said movable element, in which case the outputsignal corresponds to an absolute position of the movable element. Themotion of the magnetic field may be proportional to the motion of themovable element, in which case the output signal corresponds to arelative position of said movable element. The output signal can be usedto control a commutation sequence of a brushless DC motor mechanicallyconnected to the first movable element.

A further embodiment includes a gimbal that includes a plurality ofrotatable frame elements rotatably coupled to one another by pivotableconnections. Actuation means are coupled to rotatably connected pairs ofthe plurality of rotatable frame elements. The actuation means areoperable to rotate each of the pairs of rotatable frame elements. Thegimbal includes a plurality of first magnets, and each is affixed to arespective one of the plurality of rotatable frame elements. The gimbalincludes a plurality of first magnetic sensors each of which areconfigured and operable to detect magnetic flux density of a magneticfield produced by a respective one of the plurality of first magnets,and further operable to produce an output signal corresponding to thedetected magnetic flux. One or more second magnets are each affixed to asecondary drive element that is rotatably coupled to one of theplurality of rotatable frame elements. One or more second magneticsensors are each configured and operable to detect magnetic flux densityof a magnetic field produced by a respective one of the one or moresecond magnets, and further operable to produce an output signalcorresponding to the detected magnetic flux. The gimbal includeselectronic control means that are operable to receive the output signalsfrom the plurality of first magnetic sensors and the one or more secondmagnetic sensors and to produce a compound resolution position signal.

The actuation means may include an EMA. The plurality of first magneticsensors may include a multi-element magnetic sensor. The multi-elementmagnetic sensor may include a plurality of magneto-resistive elements.The plurality of magneto-resistive elements may include fourmagneto-resistive elements configured electrically in a bridgeconfiguration. The bridge configuration is a Wheatstone bridge. Themulti-element magnetic sensor may include a plurality of Hall effectelements. The plurality of Hall effect elements may include proportionalor digital Hall effect elements. The plurality of Hall effect elementsmay include four proportional Hall effect elements configured andarranged in an IC. The gimbal may include a high-resolution magneticsensor and a plurality of high-resolution magnets having alternatingnorth and south magnetic poles arranged in a ring around thecircumference of a motor shaft of the EMA. The high-resolution magneticsensor may be operable to measure magnetic field variations produced bymotion of the plurality of high-resolution magnet as the EMA motor shaftrotates.

DESCRIPTION OF DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings. The drawingsare not necessarily to scale, emphasis instead being placed onillustration of principles of the invention. The drawings include thefollowing figures:

FIG. 1 depicts a perspective view of an embodiment of the invention thatincludes an EMA.

FIG. 2 includes FIGS. 2A-2B, which depict an embodiment of the presentinvention including a multi-element magnetic sensor that is configuredto detect movement of a two-poled magnet.

FIG. 3 depicts a multi-element magnetic sensor according to anembodiment of the present invention.

FIG. 4 depicts a side view of an embodiment that includes an EMA andelectronic control means.

FIG. 5 includes FIGS. 5A-5C, which depict embodiments of multi-elementmagnetic sensor and magnet configurations according to the presentinvention.

FIG. 6 depicts an embodiment including an actuator motor sealed in ahousing.

FIG. 7 depicts an embodiment of a gimbal according to the presentinvention.

FIG. 8 depicts high-resolution position sensors according to anembodiment of the present invention.

FIG. 9 includes FIGS. 9A-9B, which depict top and side views,respectively, of an embodiment including a high-resolution positionsensor utilizing a magnetic flux guide.

FIG. 10 depicts a cross sectional view of an embodiment including anabsolute position sensor.

FIG. 11 depicts a cross sectional view of an embodiment including amagnetic quadrature sensor.

FIG. 12 includes FIGS. 12A-12C, which depict perspective views ofdifferent embodiments of a quadrature sensor according to the presentinvention.

FIG. 13 depicts steps in a method of measuring position according to anembodiment of the present invention.

DETAILED DESCRIPTION

The present invention may be understood by the following detaileddescription, which should be read in conjunction with the attacheddrawings. The following detailed description of certain embodiments isby way of example only and is not meant to limit the scope of thepresent invention.

Aspects of the present invention may be used to detect motion of movableelements including but not limited to machine components. Embodiments ofthe present invention couple one or more magnets to a moveable element,which when moved can produce motion and/or variations of the magneticfield and/or a magnetic flux associated with the one or more magnets,which can be detected by magnetic sensors coupled thereto. The motionand/or variations of a magnetic field and/or a magnetic flux may beproduced by any combination of a relative motion between the magneticsensors, associated magnets, or by the motion of associated magneticmaterial disposed between a magnet and a corresponding magnetic sensor.Magnetic sensors according to the invention may be capable of measuringeither rotary, or linear motion, or both. Such sensors can provideindication of an incremental position change, an absolute position, orboth. Certain aspects of the present invention provide for a combinationof absolute position sensing and high-resolution position sensing formeasurement of either linear and/or angular position. By combining twoor more magnetic sensors in a moveable machine assembly, e.g., anactuator, redundant position measurement functionality can be providedor combined at different levels of mechanical advantage in the assemblyto provide a broader range of position measurement, or highermeasurement resolution, or both. Suitable magnetic sensors include, butare not limited to, Hall effect devices and/or magneto-resistiveelements.

Certain aspects of the present invention are directed to multi-elementmagnetic sensors used for position sensing of movable elements,including but not limited to machine components. Suitable signalconditioning and/or control means such as control electronics, orelectronic controllers, can be used to receive output signals from thesensors. The motion of movable elements, such as mechanical systemsincluding actuators, can accordingly be measured and controlled.Position signals can be used in certain embodiments for desired controlfunctions. For non-limiting example, position signals obtained from oneor more multi-element magnetic sensors can be used to control thecommutation of brushless DC motors, e.g., a motor of an EMA coupled to adrive train.

FIG. 1 depicts a perspective view of a preferred embodiment 100 thatincludes an electromagnetic actuator (EMA) 105. The EMA 105 includes amagnetic sensor assembly 102 that includes multi-element magneticsensors 102 a-102 c that are configured and arranged to detect themotion of multiple magnets 104 a-104 c, respectively, that are affixedto moveable drive elements 110 a-110 c of the EMA 105. Suitable magnets104 a-104 c include permanent multi-pole magnets and/or configurationsof multiple magnets. Each of the magnetic sensors 102 a-102 c isconfigured to detect flux or variations in the magnetic field of acorresponding magnet 104 a-104 c. In certain embodiments, the sensors102 a-102 c may be included in integrated circuits (ICs), which can bemounted on a printed circuit board (PCB) 103. Output signals from themagnetic sensors may be used for compound-resolution position sensing ofthe EMA elements as described in more detail below.

During position sensing operation, one or more multi-element magneticsensors such as 102 a-102 c may provide electric signals to anelectronic control unit (not shown), which can enable the electroniccontrol unit to control a commutation sequence for a desired brushlessDC motor, e.g., an EMA motor. For such a commutation sequence, theelectronic control unit may use one or more position signals, each froma different multi-element magnetic sensor 102 a-102 c, to control outputcurrents to stator coils within the DC motor of interest. By switchingthe currents to the stator coils in a commutation sequence, the currentsin the stator coils generate magnetic fields that produce torque on ashaft of the rotor associated with the stator, causing the rotor andshaft to rotate to a desired position relative to the stator. In certainembodiments, the continuously received position signals from one or moremulti-element magnetic sensors may be used by the electronic controlunit for the commutation of a three-phase EMA motor.

The drive elements 110 a-110 d include primary drive elements 110 b-dthat receive power from a motor 106 by way of motor shaft 108, and alsoa secondary drive element 110 a that does not transfer power to anoutput element. The primary drive elements 110 b-d deliver power to aload output shaft 114 and output bearing 118 by way of a threadedconnection 112 with primary drive element 110 d. The output shaft 114has a direction of motion indicated by arrow 116. The primary orsecondary drive elements can be rotary elements, e.g. shafts, gears,screws or cranks, or linear elements, e.g. screws, links or racks. Incertain applications, a drive element, such as a link, can bothtranslate and rotate in its motion.

In operation of the EMA 105, each magnet 104 a-104 c moves with therespective drive train element 110 a-110 c to which it is affixed. Eachmagnetic sensor 102 a-102 c detects motion of the corresponding magnet104 a-104 c, and therefore also detects motion of the drive element towhich the respective magnet is attached. Electric signals produced bythe magnetic sensors 102 a-102 c may be directed to and received byelectronic control means, e.g., control electronics (not shown) forcompound-resolution position measurement described in more detail below.By adjusting the size, e.g., radii, of drive elements 110-110 c, themechanical advantage of the drive elements can be changed. This canproduce a corresponding adjustment to the output signals produced by themagnetic sensors 102 a-102 c, with a similar adjustment to thecompound-resolution of position measurement.

In some embodiments, the relative positioning of the magnets 104 a-104 cand the magnetic sensors 102 a-102 c can be reversed, wherein themagnetic sensors rotate relative to the fixed magnets. Further, incertain embodiments, the magnets and magnetic sensors can remainstationary with respect to one another and the motion of the actuatorcan cause the motion of a magnetic material that is interposed betweenor placed near the magnets and sensor. Suitable magnetic materialinclude paramagnetic and/or ferromagnetic materials, which are sometimesreferred to as “soft” and “hard” magnetic materials, respectively.

FIG. 2 includes FIGS. 2A-2B, which depict suitable sensors for positionsensing according to an embodiment 200 of the present invention. Amulti-element magnetic sensor 202 is configured and arranged to detectmovement of a magnetic field 201 of a two-poled magnet 204 attached to adrive train element, e.g., rotatable shaft 203. The multi-elementmagnetic sensor 202 may include HED and/or magneto-resistive elements.The sensor 202 may be part of an integrated circuit (IC) and packaged inan IC assembly, which may also include suitable signal conditioningelectronics. As illustrated in FIG. 2A, the multi-element magneticsensor 202 is configured and arranged to detect flux density of themagnetic field 201 produced by the two-poled magnet 204. The magnet 204may be mounted on an end of a rotatable shaft 203, e.g., one that isrotated by a machine element of an actuator. As the shaft 203 moves withrespect to a multi-element magnetic sensor 202, so too does the magneticfield, depicted by magnetic flux 201, produced by the magnet 204. Thedifferent orientations of the magnetic field 201 are detected by themulti-element magnetic sensor 202. The absolute and/or relative positionof the shaft 203 and/or mechanically connected components can bemeasured by suitable control means, such as control electronics (notshown), connected to the multi-element magnetic sensor 202. As depictedin FIG. 2 b, multiple multi-element magnetic sensors 202 a-202 d may beused in concert to facilitate averaging of a temporally and/or spatiallyvarying magnetic field, depicted by surface 201, in certain embodiments.In preferred embodiments, a rotary magnetic sensor, product numberAS5040, available from Austria Micro Systems, is used for the magneticsensor 202.

FIG. 3 depicts a multi-element magnetic sensor 302 for position sensingaccording to an alternate embodiment 300 of the present invention. Thesensor 302 includes multiple proportional magneto-resistive magneticsensors 302 a-302 d that are electrically connected to one another. Theproportional magnetic sensors 302 a-302 d are configured and arranged ina bridge configuration to sense a variable magnetic flux density that iscaused by a moving magnetic field 301. A voltage supply 304 suppliesvoltage to the proportional magnetic sensors 302 a-302 d. In certainapplications, the proportional magnetic sensors 302 a-320 d may bearranged in a suitable Wheatstone bridge, as indicated.

By being in close proximity to one another and connected in a bridgeconfiguration, such as a Wheatstone bridge, the proportional magneticsensors 302 a-302 d can be self-calibrating and/or minimize the effectsof measurement errors that are produced by a single sensor. For a bridgeconfiguration in which each sensor has a resistance that is nominallyequal, as indicated in FIG. 3 by R, environmental or mechanical factorsmay produce small variations in resistance among the sensors 302 a-302d, as indicated by ΔR. Such variations in resistance ΔR may also beproduced by local variations in the detected magnetic field 301.Resistance variations ΔR between different portions of the bridgeconfiguration produce current at 305, which leads to an equalization, oraveraging, of the resistance values of the magnetic sensors 302 a-302 d.As a result of this self-calibration capability, the proportionalmagnetic sensors 302 a-302 d can reduce or eliminate positionmeasurement errors due to temperature variations, electromagneticinterference, minor misalignment or movement of an associated magnet,and/or variation in an applied voltage 304.

FIG. 4 depicts a side view of an embodiment 400, similar to that of FIG.1, which includes an EMA 405 with magnets, sensors, and electroniccontrol means, e.g., control electronics 420 a-420 b. The EMA 405includes a motor 406 and motor shaft 408, which is operable to rotate agear train that includes multiple gears 410 a-410 d. In operation, thegear train transfers power from the EMA motor 406 to an output shaft 414by way of a power screw 412. For an assumed direction of rotation 411 a,e.g., counter-clockwise, of the motor shaft, the correspondingdirections of rotation of gears 410 a-410 c are indicated by arrows 411b-411 d. It will of course be understood that the directions of rotationdepicted will be reversed when the direction of rotation of the motoroutput shaft is reversed. The output shaft 414 has a direction of motionindicated by arrow 416.

The control electronics 420 a-420 b are connected to the multi-elementmagnetic sensors 402 a-402 b and 402 d, respectively, by suitableconnections, such as electrical connections 421 a-421 b, respectively.The control electronics 420 a-420 b may include desired logic, signalprocessing and/or signal conditioning circuitry. The control electronics420 a-420 b process and apply the signal(s) received from themulti-element magnetic sensors 402 a-402 c and 402 d, respectively, toprovide useful monitoring and/or control functionality. For example,signals received from the multi-element magnetic sensors 402 a-402 c and402 d may be used by the control electronics 420 a-420 b, respectively,to determine and control the position of an output element (not shown)coupled to output shaft 414 of an associated EMA 405. The controlelectronics 420 a-420 b may report position of sensed mechanicalcomponents to local or higher-level electronics, for example, an alarmsystem or control computer. In some embodiments, the control electronics420 a-420 b may be a single unit.

In certain situations, one or more magnetic sensors and thecorresponding magnets may be positioned away from particular componentsof a movable mechanical assembly. For example, locating the magneticsensors and the corresponding magnets apart from a motor of an EMA, mayprovide the ability to thermally isolate the sensors from heat producedby the EMA motor. Moreover, remote positioning of a sensor may bedesirable to produce one or more position signals based on movement of aparticular drive element that is spaced apart from the motor shaft orother drive elements. The ability for remote positioning of one or moremagnetic sensors may allow sensors to be placed at a convenient oraccessible locations to provide otherwise unavailable positionmeasurement. Accuracy of position measurement by magnetic sensors may beimproved, in certain embodiments, by measuring the motion of an outputelement of a mechanical system, thereby reducing the deleterious effectsof mechanical backlash. In certain embodiments, such reduction ofbacklash effects can improve servo-control dynamics.

FIG. 5 includes FIGS. 5A-5C, which respectively depict variousconfigurations of magnetic sensors 502 a-502 b and magnets 504 a-504 bfor position sensing according to embodiments 500A-500C of the presentinvention. FIG. 5A depicts an embodiment 500A that includes arepresentative actuator that includes a motor 501 and an actuator outputrod 510 coupled to the motor 501 via drive screw 512 and gears 506 and508. A rod-end bearing assembly 514 is connected to the output rod 510for connection to a moveable element. The output rod 510 has a directionof motion indicated by arrow 516. Motion of the output rod 510 isproduced by a suitable prime mover, e.g., motor 501, and the mechanicalconnection of drive screw 512 powered by gears 506 and 508. FIGS. 5B-5Cinclude broken views of the FIG. 5A, with different magnet and sensorconfigurations coupled to secondary drive elements of the actuator. Asdepicted in FIG. 5A, a multi-element magnetic sensor 502 a can beconfigured and arranged to detect the changing magnetic field ofcorresponding magnet 504 a caused by the motion of the primary driveelement 506 to which the magnet 504 a is coupled. Multi-element magneticsensor 502 a is located within magnetic proximity of a magnet 504 a,which in the embodiment shown in FIG. 5A, is affixed on the end of astub shaft attached to the motor shaft of the actuator motor 501.

Magnet and sensor assemblies may be configured and arranged to detectthe motion of not only primary drive elements, which transfer power toan output element, such as gear 506 but also secondary drive elementsthat do not transfer power to any output elements. For example, FIGS.5A-5C depict different magnet and sensor assemblies for detecting themotion of different secondary drive elements that are mechanicallyconnected to rod end 510. FIG. 5A depicts one configuration of a magnet504 b affixed to a secondary drive element including a gear 518 a. Amulti-element magnetic sensor 502 b is mounted on a base, e.g., a PCB503 b, in proximity to the magnet 504 b. Magnet 504 b is mechanicallycoupled or affixed to gear 518 a that meshes with a subsidiary gear 518b. Both gears, 518 a and 518 b, are mounted on bearings (not shown) thatallow for rotation and prevent translation of the gears. The subsidiarygear 518 b is rotated by the axial motion of drive screw 520 that isdriven by screw shank 522. The drive screw shank 522 is connected to theactuator output element 510 by a bracket 524. As the actuator outputelement 510 moves along a direction of motion, shown by arrow 516, drivescrew shank 522 is moved in the same direction. This translates drivescrew 520 that causes the rotation of gears 518 b and 518 a. The magnet504 b that is affixed or otherwise coupled to gear 518 a then rotates onan axis substantially parallel to actuator output rod 510. Outputsignals from sensors 502 a and 502 b can be combined by control means(not shown) to provide a compound-resolution position measurement of adesired movable element, e.g., output rod 510. By adjusting the radii ofthe various gears, the mechanical advantage of the drive elements can bechanged. This can produce a corresponding adjustment to the outputsignals produced by the magnetic sensor 502 a-502 b, with a similareffect on the compound-resolution in position measurement.

FIG. 5B depicts another embodiment 500B of a magnet 504 b affixed to asecondary drive element including a crankshaft and crank arm assembly518 c. The magnet 504 b is affixed to crank arm 518 c near to or on theaxis of rotation of the crankshaft and crank arm assembly 518 c. Thecrank arm assembly 518 c is connected by a pivotable connection 519 tothe shank 522 a. The shank 522 a is connected by a bracket 524 to theactuator output rod 510. As the actuator output rod 510 moves, indicatedby direction of motion 516, the crank arm 518 c and the affixed magnet504 b rotate about the axis of rotation, as indicated by arrow 526. InFIG. 5B, the rotation of the magnet 504 b is substantially perpendicularto actuator output rod 510. FIG. 5C depicts another embodiment 500C of amagnet 504 b affixed to a secondary drive element including a pinion 518e of a rack and pinion assembly. The associated rack 518 d is connectedby a bracket 524 to the actuator output rod 510. As the actuator outputrod 510 moves along a range of movement, indicated by arrow 516′, therack 518 d translates, also as indicated by arrow 516′. The magnet 504 bconsequently rotates along with pinion 518 e, as indicated by arrow 526,about an axis substantially perpendicular to the actuator output element510.

For certain applications, it may be desirable to enclose motors andother moving components of movable mechanical systems, e.g., EMAs. AnEMA motor may be sealed to inhibit unwanted leaking, in or out, offluids, gasses, EMI or magnetic fields. A sealed housing 610 can protectan EMA from a harsh environment. In certain embodiments, an EMA having amotor sealed in a housing 610 can be immersed in a fluid for wet motoroperation.

FIG. 6 depicts an embodiment 600 that includes an EMA motor 608 that issealed in a housing 610. A magnet 604 is affixed to a motor shaft 606 ofthe EMA motor 608. A multi-element magnetic sensor 602 is mounted on abase 603, e.g., a PCB, outside of the housing 610 in magnetic proximityto the magnet 604. The housing 610 may include nonmagnetic window 612positioned between the magnet 604 and the multi-element magnetic sensor602.

Because the magnetic field from the magnet 604 is unimpeded bynonmagnetic material(s) of the window 612, the multi-element magneticsensor 602 will operate through the nonmagnetic window 612. Suitablenonmagnetic materials for the window 612, include but are not limited totitanium, certain nonmagnetic ceramic materials, and/or plasticmaterials. In certain high-speed embodiments, the window 612 may be madeof a non-electrically conducting material, e.g., a nonmagnetic ceramicmaterials or plastic material, to avoid the magnetic field attenuationresulting from the counteracting field produced by eddy currents in anelectrically conducting material.

Embodiments of the present invention may provide forcompound-resolution, e.g. dual-speed resolution, position measurement ofmovable elements. For example, dual-speed resolving capability can beprovided by using two or more multi-element magnetic sensors to sensethe movement of different power train elements that undergo dissimilarmovement. For example, two or more multi-element magnetic sensors may beconfigured to detect the movement, respectively, of gears havingdifferent gear diameters. Such gears in a gear train move at differentspeeds relative to an associated machine component such as actuatoroutput element.

FIG. 7 depicts a further embodiment directed to dual resolution positionmeasurement in a gimbal 700. The gimbal 700 includes three rotatableframe elements 706 a-706 c that are pivotable connected to one another.Magnetic sensors 702 a-702 f and associated magnets 704 a-704 f areconfigured to measure position of the frame elements 706 a-706 c duringoperation of the gimbal 700. Actuation means, for example EMAs 708 a-708c, are mechanically connected, either directly or indirectly, to arespective one of the three frame elements 706 a-706 c. By controllingthe EMAs 708 a-708 c, alone or in combination, the frame elements 706a-706 c can be rotated about their respective axes. A desired componentor device that is held by the frame elements 706 a-706 c can accordinglybe oriented in any desired direction. Signals produced by themulti-element magnetic sensors 702 a-702 f may be used to sense themotion of the gimbal 700 and to control motor commutation of the EMAs708 a-708 c. Control means such as an electronic control unit (notshown) may control the position of the gimbal 700 by regulating orselectively applying power signals to one or more of the EMAs 708 a-708c.

Each frame element may be pivotably connected to the others by one ormore suitable pivotable connections 709 so that as an EMA motoroperates, one of the frame elements moves with respect to two pivotablyconnected frame element. As configured in FIG. 7, frame element 706 ahas a single pivotable connection 709 to frame element 706 c and twopivotable connections 709 to frame element 706 b. Frame element 706 bhas two pivotable connection 709 to frame element 706 c. In certainembodiments, a suitable pivotable connection 709 may include an EMAmotor shaft e.g., shaft 708 b′, that is fixed to one frame element,e.g., frame element 706 c, with the housing of the associated motor EMA708 b being fixed to another frame element, e.g., frame element 706 b.Suitable bushings and/or bearings may be included in a pivotableconnection 709 used in the gimbal 700. It should be understood thatalthough the gimbal 700 is depicted as having three rotatable frameelements 706 a-706 c, a gimbal according to the present invention mayhave any desired number of rotatable frame elements, e.g., one, two, ormore than three, etc.

Certain of the magnets 704 a, 704 d, and 704 e, are preferably mountedon ends of motor shafts of the EMAs 708 a-708 c to detect the motionbetween the associated frame elements and the EMA motor shafts duringmovement of the gimbal 700. Corresponding magnetic sensors, which may besingle or multi-element magnetic sensors, may be affixed to the frameelements 706 a-706 c. When a magnet is mounted to an EMA motor outputshaft, the corresponding magnetic sensor directly detects, e.g., with a1:1 ratio, the motion of the EMA output shaft magnet.

Each rotatable frame element 706 a-706 b of the gimbal 700 may have morethan one magnetic sensor and magnet for position sensing with acombined, e.g., dual-speed, resolution. For example, in certainembodiments, one or more sensors, e.g., 702 b, 702 c, and 702 f, detectmovement of corresponding magnets, 702 b, 702 c, and 702 f, that areattached to power train elements, 712 a-712 c, that move at differentspeeds than the output shafts of respective EMAs 708 a-708 c. Suchconfigurations can provide compound-resolution, e.g., dual-resolution,for the position sensing of the various frame elements of the gimbal700. By suitable design of the geometry of the mechanical connectionbetween higher-speed and lower-speed sensors, a desired level ofresolution of position measurement can be provided in conjunction withabsolute position measurement. To monitor position beyond one turn of amagnet, e.g., 704 f, external circuitry may be used to count the numberof index pulses that indicate the number of turns of the magnet.

As previously described, certain embodiments of the invention mayprovide high-resolution magnetic sensing and absolute position magneticsensing in combination, e.g., over a broad range of motion. For example,it may be desirable to measure the absolute position over the full rangeof the actuator at the output element, and at the same time anothermagnetic sensor and magnet monitors the motion of another machineelement, e.g., the motor shaft, to provide much higher resolution. Suchfunctionality may be desirable to ascertain both a high resolution andabsolute position and full range of motion of a movable element, e.g., amechanical component. In certain embodiments, one or more magneticsensors, e.g., a Hall effect or magneto-resistive device, may beutilized for high-resolution position sensing. Suitable sensors forhigh-resolution position measurement may be configured to produce eitherdigital or analog signals.

FIG. 8 depicts a suitable magnet and sensor configuration according to afurther embodiment 800 of the present invention that includes twohigh-resolution magnetic position sensors 802 a-802 b. Suchhigh-resolution position sensors may be suitable for use with anabsolute position sensor. Each magnetic sensor 802 a-802 b is in closeproximity to a ring configuration 804 that includes a plurality ofmagnets 803 disposed about the perimeter of ring 804. The ring 804 isaffixed or connected to a rotatable element, such as an actuator motorshaft or the like. Representative north (N) and south (S) poles of themagnets 803 are indicated. The magnets 803 may be individual magnetsarranged on a shaft or North and South poles applied in a solid ring ofmagnetic material. The magnetic poles can be either tightly spaced,which may be desirable for a digital type sensor, or the poles may bewidely spaced and sensed in an analog fashion. In certain embodiments, apair of magnetic yokes 806 a-806 b may be used to direct magnetic fluxto a sensor 802 a, as indicated.

FIG. 9 includes FIGS. 9A-9B, which depict top and side views,respectively, a high-resolution position sensor utilizing a magneticflux guide, according to a further embodiment 900 of the presentinvention. Such high-resolution sensors may desirable to measureposition of rotatable shafts, for example EMA motor shafts. The fluxguide channels magnetic flux from a single dipole magnet 904 to anassociated magnetic sensor 902. The flux guide includes a toothedmagnetic guide ring 906 configured around and fixed to a shaft 901,which may be a motor or drive train shaft or the like. The flux guidealso includes a toothed guide yoke 908 configured and adapted to thetoothed guide ring 906. A yoke piece 910 may be positioned to extendfrom the magnetic sensor over the toothed guide ring 906 in certainembodiments. As the shaft 901 is rotated, the displacement of the teethof the toothed guide ring 906 relative to the teeth of the toothed guideyoke 908 causes flux variations that are detected by the sensor 902. Incertain embodiments, a magnet array and toothed flux guide may be laidout linearly to detect flux variations due to linear movement.

As described above, certain embodiments of the invention can include acombination of one or more proportional magnetic sensors for absoluteposition sensing that are used in conjunction with one or more magneticsensors for high-resolution position sensing. FIG. 10 depicts anabsolute position sensor 1002 according to an embodiment 1000 of thepresent invention. The sensor 1002 is configured and arranged to detectflux density from an associated magnet 1004 to sense the motion of anassociated mechanical element, e.g., translatable actuator output shaft1007. The sensor may be affixed to the machine element in someapplications. In other applications, the magnet may be affixed to themachine element 1007. The sensor 1002 may be an analog, or continuousresolution, absolute magnetic sensor, e.g., a Hall effect device ormagneto-resistive element. Flux from the associated magnet 1004 isconducted to the sensor 1002 by a pair of magnetic yokes 1006 a-1006 b.Translation of the sensor 1002 and the high magnetically permeable yokes1006 a-1006 b with respect to the magnet 1004 causes the flux density atthe sensor 1002 to vary in a detectable fashion.

In certain embodiments, a range of detection of the sensor 1002 wouldtypically cover the full extent of motion of an associated moveableelement, e.g., an actuator, as indicated by arrow 1001. The sensor 1002may be mechanically linked to the output of an actuator in a way thatapproximately relates the full range of actuator motion to the fullrange of the sensor. The sensor 1002 is preferably a single Hall effectdevice or magneto-resistive element, though the sensor 1002 can be amulti-element magnetic sensor.

Variations of flux at the sensor 1002 can be accomplished by moving themagnet 104 relative to the sensor 1002, or vice versa, with out anyintervening flux guide or yokes in certain embodiments. Flux Variationsat the sensor 1002 may be detected by moving a flux guide in a fashionto channel the flux more or less to the sensor 1002. Further, a magneticelement can be moved in a manner to obscure or attenuate the magneticflux that is delivered to the sensor 1002. This can be done with onepair of magnet and sensor, or multiple magnets (e.g. to increase rangeor resolution), or multiple sensors or a multiple of both magnets andsensors. Output signals from a sensor 1002 are routed to electroniccontrol means, such as sensing and control electronics, as shown in FIG.6. The output signals may be used for a desired purpose such as toreport or control position of a moveable element.

In certain embodiments, an absolute position sensor can be configured ina rotary, or circular, fashion similarly to the linear configurationdescribed with respect to FIG. 10. For a circular absolute positionsensor, a sensing sequence may be repeated after a full 360 degrees ofrotation. FIG. 11 depicts a cross sectional view of a magneticquadrature sensor 1101 according to a further embodiment 1100 of thepresent invention. Such quadrature sensors may desirable to measureposition of rotatable shafts, for example EMA motor shafts. Thequadrature sensor 1101 includes two or more magnetic sensors 1102 suchas Hall effect devices or magneto-resistive elements (one sensor isomitted for clarity). A suitable magnetic sensor may be single-elementsensor or a multi-elements sensor. Each magnetic sensor 1102 ispositioned between a pair of yokes 1104 a-1104 b that are made of amagnetically conductive material. Each yoke 1104 a-1104 b is adapted tothe circumference of a rotatable shaft 1106, which can be part of thedrive train of an actuator or movable machine assembly. A permanentmagnet 1108, or other magnetic material, is configured on thecircumference of the shaft 1106.

As the shaft 1106 rotates, the sensor 1102 detects the movement of themagnetic field produced by the magnet 1108. By having a second sensor1102 and pair of yokes positioned 90 degrees apart from the first sensorand pair of yokes along the circumference of the shaft, e.g., asdepicted in FIG. 12A, a quadrature signal is obtained as the shaftrotates. The magnetic quadrature sensor 1100 provides the ability forself-calibration and common mode noise reduction. The 1100 sensor may beused as a high-resolution or low-resolution sensor, and may provideabsolute or relative position sensing. Electronic control means (notshown), such as an electronic control unit, operable to provide sinewave quadrature decoding may be used to decode the quadrature signals.Embodiments including a magnetic quadrature sensor 1100 may be desirablein applications where access to an end of a rotatable shaft is difficultor impossible. Alternatively, the shaft 1106 may be magnetizeddiametrically to form a magnetic dipole so that magnet 1108 is notneeded.

FIG. 12 includes FIGS. 12A-12C, which depict different configurations ofa quadrature sensor 1200 used for absolute position sensing according toan embodiment of the present invention. The quadrature sensor includestwo magnetic sensors 1202 a-1202 b, such as Hall effect devices,arranged 90 degrees apart along the circumference of a rotatable shaft1206. Each sensor is located between ends of a pair of yokes that areadapted to the shaft. FIG. 12A depicts a perspective view of anembodiment including a two-pole magnet. FIG. 12B depicts a perspectiveview of an embodiment including a four-pole magnet. FIG. 12C depicts aperspective view of an embodiment including an alternate configurationof a four-pole magnet.

FIG. 13 depicts steps in a method 1300 of sensing position according tothe present invention. Motion of a movable element of a plurality ofmovable elements is produced, as described at step 1302. The pluralityof moveable elements can for example, be part of a drive train such asan actuator drive train. Such motion may be produced by a desired typeof prime mover, such as various types of actuators including, but notlimited to, EMAs, hydraulic actuators, pneumatic actuators, etc. Motionof a first magnetic field is produced, as described at step 1304,relative to a first magnetic sensor by the motion of the movableelement. Movement of the magnet, an interposed magnetically conductiveparamagnetic material, and/or the magnetic sensor may cause the motionof the magnetic field. Motion of a second magnetic field is produced, asdescribed at step 1306, relative to a second magnetic sensor by themotion of the movable element. Flux or variations in the magnetic fieldsare detected, as described at step 1308. An output signal correspondingto the variations in the magnetic fields is produced, as described atstep 1310. A position of the moveable element is measured, as describedat step 1312, and may have compound resolution, e.g., dual-speedresolution.

The motion of the movable element, as described at step 1302, mayinclude moving an actuator output element. The motion of the magneticfield, as described at step 1304, may be produced by moving a magnet,for example by rotating the magnet. The motion of the magnetic field, asdescribed at step 1304, may be produced by moving a multi-elementmagnetic sensor, for example by rotating the sensor. The detection ofvariations in the magnetic field, as described at step 1308, may includeusing a magnetic quadrature sensor. The output signal produced, asdescribed at step 1310, may correspond to an absolute position and/orrelative position of the movable element. The output signal may be usedto control a commutation sequence of a brushless DC motor mechanicallyconnected to the movable element.

Accordingly, embodiments of the present invention may offer variousadvantages over the prior art. Multi-element magnetic sensors accordingto the present invention can provide indication of both incrementalposition change and absolute position. Redundancy of position sensorfunctionality may be provided by use of two or more multi-elementmagnetic sensors. Redundancy may be desirable certain applications wherehigh-reliability is required. Embodiments may be used to sense positionin an actuation device or movable machine assembly to provide ameasurement from which to control the device, e.g., a servoactuator,and/or to report the position to local or higher-level electronics,e.g., an alarm system or control computer. Embodiments may be used toprovide low cost, durability, low weight, small volume and/or remotesensing capabilities for servoactuators. Embodiments may includeactuators with simple position control, e.g., end of stroke electronicstops.

Certain embodiments may be applied to aerodynamic control surfaceactuators, aircraft utility actuators, single axis and multi axisgimbals and EMAs. The actuators can be hydraulic, pneumatic or electricin nature. The prime movers of such actuators may be of any suitabletype, e.g., motors, pistons, solenoids or voice coils, and the like.Multi-element position sensors according to certain embodiments asinstalled onto single and multi-axis gimbals in preferred embodiments toreduce cost and weight while maintaining or increasing position accuracyover such devices as rotary variable differential transformers (RVDTs),potentiometers, and resolvers.

Moreover, embodiments of the present invention may be advantageouslyused as alternatives to synchros, resolvers, RVDTs, linear variabledifferential transformers (LVDTs), and potentiometers. These sensorsprovide the same at lower cost and in a smaller and more flexiblefootprint. For applications using brushless DC motors these sensors andassociated control electronics can be used to provide the requisitecommutation sequencing. The high-resolution position sensing provided bythese sensors allow for sine drive type commutation that can reducetorque ripple and improve the effective use of motor torque capability.Embodiments can provide for remote location of a position sensor. Remoteposition sensing can provide advantages including (i) the ability tothermally isolate the sensor, (ii) the ability to produce an outputsignal that is based on a particular drive element, and/or (iii) and theability to locate the sensor at a convenient or accessible location.

While the present invention has been particularly shown and describedwith references to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A method of measuring position of a moveable element of a drive trainhaving a plurality of movable elements, said method comprising the stepsof: producing motion of a movable element of said plurality of movableelements; producing motion of a first magnetic field relative to a firstmagnetic sensor by said motion of said moveable element; producingmotion of a second magnetic field relative to a second magnetic sensorby said motion of said moveable element; detecting variations in saidmagnetic fields; producing an output signal corresponding to saidvariations in said first and second magnetic fields; determining aposition of said moveable element as a function of said variations insaid first and second magnetic fields; and adjusting the position of themovable element based upon the detected variations in the magneticfields.
 2. The method of claim 1, wherein said step of producing motionof a movable element includes a step of moving an actuator outputelement.
 3. The method of claim 1, wherein said step of producing motionof a magnetic field comprises a step of moving a magnet affixed to saidmovable element.
 4. The method of claim 1, wherein said step ofproducing motion of a magnetic field comprises a step of moving saidfirst magnetic sensor.
 5. The method of claim 1, wherein said motion ofsaid magnetic field corresponds directly to said motion of said movableelement, whereby said output signal corresponds to an absolute positionof said movable element.
 6. The method of claim 1, wherein said motionof said magnetic field is proportional to said motion of said movableelement, whereby said output signal corresponds to a relative positionof said movable element.
 7. The method of claim 1 wherein adjustingcomprises transmitting a power signal to a motor coupled to the movableelement in response to detecting the position of the moveable elementand as a function of the variation in the magnetic field based upon thedetected variations in the magnetic fields.
 8. The method of claim 1,further comprising detecting a position of an output element moveablycoupled to the moveable element of the drive train based upon thedetected variations in the magnetic fields.
 9. A method of detecting aposition of a moveable element coupled to a drive train, comprising:moving the moveable element of the drive train to produce a motion of amagnetic field relative to a magnetic sensor; receiving an output signalcorresponding to a variation in the magnetic field detected by themagnetic sensor; detecting a position of the moveable element as afunction of the variation in the magnetic field based upon the outputsignal; and adjusting the position of the movable element as a functionof the variation in the magnetic field based upon the output signal. 10.The method of claim 9 wherein adjusting comprises transmitting a powersignal to a motor coupled to the movable element in response todetecting the position of the moveable element and as a function of thevariation in the magnetic field based upon the output signal.
 11. Themethod of claim 9, further comprising transmitting a power signal to abrushless DC motor mechanically coupled to the first movable element inresponse to detecting the position of the moveable element as a functionof the variation in the magnetic field based upon the output signal, theoutput signal operable control a commutation sequence of the brushlessDC motor.
 12. The method of claim 9, further comprising detecting aposition of an output element moveably coupled to the moveable elementof the drive train based upon the detected position of the moveableelement.
 13. The method of claim 9, wherein moving comprises moving afirst moveable element of the drive train to produce a motion of a firstmagnetic field relative to a first magnetic sensor and to generatemotion of a second moveable element of the drive train to produce amotion of a second magnetic field relative to a second magnetic sensor;receiving comprises receiving a first output signal corresponding to avariation in the first magnetic field detected by the first magneticsensor and receiving a second output signal corresponding to a variationin the second magnetic field detected by the second magnetic sensor; anddetecting comprises detecting a position of the first moveable elementof the drive train as a function of the variation in the first magneticfield based upon the first output signal, detecting a second position ofthe second moveable element of the drive train as a function of thevariation in the second magnetic field based upon the second outputsignal, and detecting a position of an output element moveably coupledto at least one of the first moveable element and the second movableelement of the drive train based upon the first output signal and thesecond output signal.
 14. A method of measuring position of a moveableelement of a drive train having a plurality of movable elements, saidmethod comprising the steps of: producing motion of a movable element ofsaid plurality of movable elements; producing motion of a first magneticfield relative to a first magnetic sensor by said motion of saidmoveable element; producing motion of a second magnetic field relativeto a second magnetic sensor by said motion of said moveable element;detecting variations in said magnetic fields; producing an output signalcorresponding to said variations in said first and second magneticfields; determining a position of said moveable element as a function ofsaid variations in said first and second magnetic fields; and using saidoutput signal to control a commutation sequence of a brushless DC motormechanically connected to said first movable element.
 15. The method ofclaim 1, wherein: producing motion of the movable element of saidplurality of movable elements comprises producing motion of the a driveelement of said plurality of movable elements; producing motion of thefirst magnetic field relative to the first magnetic sensor by saidmotion of said moveable element comprises moving a first moveableelement of the drive train relative to the first magnetic sensor, thefirst moveable element having a magnet, to produce a motion of the firstmagnetic field; producing motion of the second magnetic field relativeto the second magnetic sensor by said motion of said moveable elementcomprises moving a second moveable element of the drive train relativeto the second magnetic sensor, the second moveable element having amagnet, to produce a motion of the second magnetic field; anddetermining the position of said moveable element as a function of saidvariations in said first and second magnetic fields comprises: receivinga first output signal from the first magnetic sensor corresponding tothe motion of the first magnetic field detected by the first magneticsensor and receiving a second output signal corresponding to the motionof the second magnetic field detected by the second magnetic sensor; anddetecting a position of the drive element as a function of a variationin the first magnetic field and the second magnetic field based upon thefirst output signal and the second output signal.
 16. The method ofclaim 15 comprising, in response to detecting the position of the atleast one of the first moveable element and the second moveable element,detecting a position of an output element coupled to the drive train.17. The method of claim 16 comprising, in response to detecting theposition of the output element coupled to the drive train, controlling aposition of the output element coupled to the drive train.